In the instant application, the power plant comprises (includes, but is not necessarily limited to) an internal combustion engine, a disk clutch and gearbox of the vehicle, and a drive line including the engine, the gearbox and drive (driving) wheels.
Automatic gearboxes of the automated multi-stage gearbox type have become increasingly common in heavy-duty vehicles as microcomputer technology further develops making it possible, with a control computer and a number of actuators such as servo motors, to precision-regulate engine speed, engagement and disengagement of an automated disk-clutch between the engine and the gearbox and also the coupling means of the gearbox in relation to one another so that soft shifting is always obtained at the correct engine speed. Among others, advantages of this type of automatic gearbox (compared to a conventional automatic gearbox that is constructed with planetary gear stages and with a hydrodynamic torque converter on the input side) include: (1) the arrangement is more simple and robust, particularly with respect to heavy-duty vehicles, and can be manufactured at a considerably lower cost than a conventional automatic gearbox, and (2) the arrangement and method have higher than conventional efficiency which means lower fuel consumption is possible.
A multi-stage gearbox is usually made up of an input shaft, an intermediate shaft, which has at least one gearwheel in engagement with a gearwheel on the input shaft, and a main shaft with gearwheels which engage with gearwheels on the intermediate shaft. The main shaft is also connected to an output shaft coupled to the driving wheels via, for example, a drive shaft.
Each pair of gearwheels has a different ratio compared with another pair of gearwheels in the gearbox.
Different gears are obtained by virtue of different pairs of gearwheels transmitting the torque from the engine to the driving wheels. Each gear is usually synchronized, but variants exist where at least some gears are unsynchronized. Speed adaptation must then be effected in another way and with great precision, for example by means of an intermediate shaft brake (speed reduction of the intermediate shaft) or control of the engine speed (speed increase/reduction). An intermediate shaft brake adapts the speed of the intermediate shaft relatively rapidly to the new lower ratio to be selected; that is to say, intermediate shaft braking takes place during upshifting.
Electronic control systems for the engine of a vehicle have also been affected by the development of computer technology and have become more accurate, more rapid and more adaptable to prevailing states of the engine and the surrounding environment. The entire combustion process can be precision-controlled according to each operating situation. The speed of the engine can therefore be controlled accurately. An engine can also be equipped with an engine-braking device to be used primarily as an auxiliary brake. Auxiliary brakes are used chiefly in heavy-duty vehicles with the major purpose of sparing the service brakes of the vehicle, in particular on long downhill gradients when it is desirable to brake in order to maintain a reasonably constant speed.
The term engine-braking device includes several different types of engine brakes. Examples of engine brakes are compression brakes, exhaust brakes (valve in the exhaust pipe), electric motor/generator coupled to, for example, the output shaft of the internal combustion engine which is also referred to as an Integrated Starter Alternator.
In addition to using the engine-braking device for braking the vehicle itself, that is to say as a supplement to the wheel brakes of the vehicle, it is known to use the engine-braking device, for example a compression brake, during shifting in vehicles with a multi-stage (usually automated) gearbox. By braking the rotation of the engine by means of the engine-braking device, more rapid speed adaptation from a high speed to a lower speed can be effected. FIG. 1 shows the fundamental phases in connection with upshifting, that is to say shifting to a higher gear with a lower ratio.
FIG. 1 shows a comparison between engine torque and the rotational speed of the engine in relation to time for a given engine type.
According to FIG. 1, phase “a” indicates a normal driving state which exists before shifting is initiated. Phase “b” shows the removal of engine torque as soon as it has been determined that upshifting is to take place; that is to say, a claw coupling (coupling sleeve) engaged for the existing gear becomes torqueless. Phase “c” shows disengagement of the claw coupling. Phase “d” shows a reduction of the rotational speed of the engine in order to adapt the rotational speed of the engine to the new gear ratio to be selected. As soon as the rotational speed of the engine has been adapted, it is possible to begin driving the vehicle with the new gear. Phase “e” therefore shows the engagement of the new claw coupling belonging to the new gear selected. Phase “f” shows the restoration of engine torque, and phase “g” shows a normal driving state after upshifting has taken place. Note that the disk clutch between the engine and the gearbox is not disengaged during upshifting but the crankshaft of the engine is coupled together with the intermediate shaft so that the engine-braking device adapts the speed of both the engine and the intermediate shaft. Relatively accurate speed adaptation is therefore necessary in order that upshifting does not feel uncomfortable. The accuracy of the speed adaptation is even more important when shifting to unsynchronized gears.
In order to shorten the discontinuation of driving power of the vehicle during upshifting, it is an advantage if the speed of the engine can be adapted to the new gear as soon as possible. This is particularly advantageous on uphill gradients when the vehicle loses more speed when driving power is discontinued, and therefore quick upshifting is required. SE 502154 discloses an exhaust brake that is selectively actuated during upshifting when certain operational parameters are reached so as to bring about rapid reduction of the engine speed during the upshifting procedure. In this way, it is said that the wear on the exhaust-braking system is reduced because the exhaust brake is introduced during only a small proportion of the total number of upshifts.
An arrangement for engine-braking in connection with an internal combustion engine is previously known from SE 9804439-9. This arrangement is adapted for engine-braking by reduction of the speed of the engine during upshifting and to this end comprises a special device sensitive to a signal generated in response to a need to bring about shifting, and in order to bring about take-up of a valve clearance in a rocker arm.
An automated disk-clutch as described above (that is to say, arranged between the engine and the gearbox) is usually regulated by means of information about the position of the throttle lever, the rotational speed of the engine, the outgoing torque of the engine and the position of the disk clutch. The controlling parameter for the position of the clutch and thus the degree of engagement between the engine and the gearbox is chiefly how the driver (alternatively a cruise control arrangement) positions the throttle lever.
One disadvantage of using engine-braking devices in order to adapt speed during upshifting is that the internal combustion engine has to be brought into a relatively narrow speed range (for example from 1600 to 1200, plus or minus 50 rpm) in order to make possible comfortable engagement of the new gear. After the speed adaptation of the engine has been carried out, the gear-engagement servo itself requires a certain reaction time before the engine can begin to deliver positive driving torque to the input shaft of the gearbox. Moreover, idle times in the engine-braking function itself can mean that it is necessary to include a safety margin when driving the vehicle uphill, which makes the average speed of the vehicle worse.
The disadvantage of using an intermediate shaft brake during upshifting is that the speed of the internal combustion engine and the speed of the input shaft of the gearbox are not synchronous when the intermediate shaft brake has carried out the speed synchronization for the new gear and the new gear has been engaged. It is then necessary afterwards to use the disk clutch between the engine and the gearbox in order to synchronize the speed difference between the engine and the input shaft of the gearbox. If this synchronization does not take place relatively slowly, too great a positive torque is obtained in the drive line, which would otherwise, if synchronization were too rapid, lead to the vehicle jerking and the drive line being subjected to unnecessary stresses. Moreover, on account of the jerks, the comfort in the vehicle is reduced.
Long shifting stages (large speed difference between engine and input shaft) therefore tend to take a long time.
There is therefore a need in vehicles equipped with multi-stage gearboxes to find an upshifting solution which can perform speed adaptation for a new gear selected in a more rapid but still comfortable way.